Incandescent lamps are commonly used as light sources for both residential and commercial facilities. However, incandescent lamps are inefficient because 90% of the input energy is lost primarily in the form of heat or infrared energy. Compact fluorescent lamps (CFL) are alternative to incandescent lamps. CFL is more effective at converting electricity into light, but it contains toxic materials which lead to environmental pollution. One solution to improve the efficiency of lamps is to use solid state devices such as light-emitting diode (LED) to produce the light.
The light-emitting diode (LED) is a solid state semiconductor device. A structure of the light-emitting diode (LED) comprises a p-type semiconductor layer, an n-type semiconductor layer, and a light-emitting layer. The light-emitting layer is formed between the p-type semiconductor layer and the n-type semiconductor layer. The structure of the LED generally comprises III-V group compound semiconductor such as gallium phosphide, gallium arsenide, or gallium nitride. The light-emitting principle of the LED is the transformation of electrical energy to optical energy by applying electrical current to the p-n junction to generate electrons and holes. Then, the LED emits light when the electrons and the holes combine.